Glutamatergic synapses are the most prevelent excitatory synapses in the central nervous system. In addition to their roles in some forms of epilepsy and excitotoxicity, glutamate receptors have been implicated in activity-dependent developmental processes and synaptic plasticity. Little is known, however, about the physiological behavior of the NMDA- or AMPA-subtype glutamate receptors at newly-forming synapses or about the physiological behavior of these synapses as a function of development. The questions outlined in this proposal address fundamental issues that need to be examined in order for a better understanding of glutamate receptors, newly-formed synapses and synaptogenetic processes. The experiments will examine functioning glutamate receptors and glutamatergic synaptic transmission in cultured rat hippocampal neurons. The specific aims are: 1) determining physiological differences between populations of synaptic and extrasynaptic receptors; 2) determining the intrinsic requirements for clustering of glutamate receptors at newly- forming synapses; 3) determining the behavior of newly-forming synapses with respect to glutamate receptor complement and release probability. Results from the first aim will allow us to monitor the formation of clusters and determine if glutamate receptors show a synaptic phenotype in response to experimental manipulation. The second aim identifies the causitive agent in activity-dependent synapse formation. Results from the final aim are intrinsically interesting but they also allow us to ask if synapse formation in hippocampal cells in culture is stochastic or determinative.